During the development of Long Term Evolution (LTE), there was much discussion for the flexibility to customize LTE to maximize performance in specific environments. Also, during discussions of LTE-Advanced (LTE-A), many suggestions were made to manage interference level by using coordinated transmissions from different cells (see Ericsson, R1-082469, “LTE-Advanced—Coordinated Multipoint transmission/reception”, Warsaw, Poland, Jun. 30-Jul. 4, 2008). It is well known that as cell size is decreased in an effort to improve spectral efficiency, interference increases.
In general, wireless communications systems using beamforming make use of a number of transmit and/or receive antennas and signal processing to create fixed or adaptive transmit/receive beampatterns. The beampatterns may have a directional nature that may result in a performance improvement when compared with unidirectional transmit and/or receive antennas. The use of the beampatterns may yield a transmit/receive gain over wireless communications systems using unidirectional transmit and/or receive antennas.
As such, beamforming has been promoted as a promising technique to increase cell coverage and to improve cell edge spectral efficiencies. However, one main drawback of beamforming is the so called flashlight effect where the channel quality changes between user equipment (UE) measurement and reporting, and NodeB (NB) transmission, due to the changes in the beampattern of the interfering neighbouring cells. Coordinated beamforming/switching has been suggested as a possible solution to this problem (see C80216m-08—487, Alcatel_Lucent, “Grid-of-Beams (GoB) Based Downlink Multi-User MIMO”, IEEE802.16m, May 2008 and NTT DoCoMo, “Proposals for LTE-Advanced technologies”, R1-082575, Warsaw, Poland, Jun. 30-Jul. 4, 2008 which are incorporated herein by reference).
What is needed is a system and method for coordinated beam switching where the coordination between cells is limited and typically changes slowly. For example, each NB in a cluster could systematically cycle through its preferred set of beams on antenna port five (5). The cycling patterns may change on a slow basis and may be a function of traffic distribution, wherein the distribution should only change on the order of seconds. This implies that the received signal and interference to noise ratio (SINR) of a slow moving UE may fluctuate deterministically in time as the different NBs cycle through their beams. The reported CQI will therefore be valid at some known time in the future given that the UE is moving slowly relative to the cycling period.